[China Aluminum Industry Network] The practice of applying secondary zinc immersion before electroless nickel plating on aluminum alloys is quite common. However, this method has significant drawbacks. First, the zinc layer tends to dissolve easily in acidic electroless nickel plating solutions. Second, due to the inclusion of zinc between the substrate and the nickel layer, galvanic corrosion (Al-Zn-Ni) occurs within the corrosive medium, leading to blisters or peeling of the coating, which ultimately reduces its corrosion resistance. Third, after zinc immersion followed by electroless nickel plating, heat treatment at 400°C is not recommended as it causes zinc leaching and creates voids. Additionally, the significant difference in thermal expansion coefficients between aluminum and nickel leads to substantial stress at high temperatures, causing cracks between the coating and the aluminum substrate.
An alternative approach using activation treatment instead of zinc immersion offers a superior base layer for electroless nickel plating. This method provides the same excellent bonding results as zinc immersion and represents a valuable innovation in pre-treating aluminum alloys.
For the activation treatment solution, the recipe typically includes NiSO4·6H2O at 24-30 g/L, HEDP at 40-50 g/L, stabilizer N at 25-30 ml/L, with pH adjusted to greater than 12 using NaOH, all at room temperature, for a duration of 1-4 minutes. The key lies in controlling the activation time. For a given formulation, the optimal immersion time can be determined experimentally, specifically when the surface achieves a uniform matte gray appearance. This ensures better quality when electroless nickel plating is applied subsequently.
Beyond these technical details, it's important to note that modern industrial practices are increasingly favoring environmentally friendly methods. The shift toward activation treatments aligns with global trends toward sustainability, reducing waste, and improving efficiency. As industries continue to evolve, embracing such innovations not only enhances product durability but also aligns with broader goals of reducing environmental impact. Thus, adopting activation treatment over traditional zinc immersion is not just a technological advancement but a forward-thinking choice that benefits both manufacturers and consumers alike.
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